Touch sensors, for example, capacitive sensors and field effect sensors, have long been used as replacements for electromechanical switches. Unlike electro-mechanical switches, which typically include a pair of electrical contacts that can be closed and opened to make and break an electrical circuit, touch sensors typically include one or more sensing electrodes and electronic circuitry to detect and respond to the presence of, for example, a user's fingertip near or at the sensing electrode. Touch sensors can detect the proximity or presence of certain other objects, including certain liquids.
Touch sensors represent an improvement over electromechanical switches in many ways. For one, touch sensors typically have no moving contacts that can wear out. For another, they can be embodied in a form that makes them relatively impervious to adverse environmental effects.
Touch sensors, however, have limited application in that there are some objects or loose, bulk materials that they might not be able to reliably detect. For example, touch sensors might not be able to reliably detect the proximity of coffee beans or other non-conductive objects. As such, touch sensors might not be preferred replacements for other types of switches and sensors adapted to detect such objects.